Three-way and four-way switches are used in electrical circuits to toggle voltage to an electrical device, most often a lighting fixture, from two or more locations. For example, two three-way switches can be used to control a light at the top of a stairway from both the top and bottom of the stairway. When more than two switch locations are required to control the electrical load, any number of four-way switches are used between the two three-way switches in the electrical circuit, e.g., an electrical circuit requiring five switches to control a single light fixture would contain two three-way switches and three four-way switches.
In a electrical circuit containing a single switch, the task of determining whether the circuit is supplying voltage to the electrical load device in the electrical circuit is a simple one. Typically if the switch is “up”, it indicates that voltage is being supplied to the load—the switch is in the “on” position, and if the switch is “down”, it indicates that voltage is not being supplied to the load—the switch is in the “off” position. Additionally the words “ON” and “OFF” are typically visible on the moveable portion of the standard wall switch. If an indicator light, designed to show when voltage is being supplied to the load, were present in a standard single-pole single throw (SPST) wall switch, a circuit within the switch could easily supply the appropriate voltage to the indicator light by tapping the terminal connected to the load-side “hot” wire, causing the indicator light to illuminate when the switch supplies AC mains voltage (“line voltage”) to the load.
Three-way switches and four-way switches however do not contain the words “ON” or “OFF” because any switch in the electrical circuit could either be in the “up” or “down” position when voltage is being supplied to the load, depending on the position(s) of the other switch(es) in the electrical circuit. Sometimes one can simply observe the load device that the switch is controlling to determine whether voltage is being supplied i.e., look at the lighting fixture to visually determine whether the light bulb is illuminated. At other times, observation is not feasible, not practical, or not possible.
Providing an indicator at each switch in a electrical circuit containing three-way or three-way and four-way switches that shows when voltage is being supplied to the load is a challenge in that in the most used wiring configuration for three-way and four way switches, whether voltage is being supplied to the load device in the electrical circuit is only “known” to one switch, the switch adjacent to the load—if the “common” terminal on the load-side three-way switch has voltage, then voltage is being supplied to the load. All other switches in the electrical circuit would have to be “told” whether voltage is being supplied to the load.
When using “conventional wiring” for circuits containing three-way and four-way switches, each three-way and four-way switch in the electrical circuit is connected to the next switch in the electrical circuit by two “traveler wires” or “travelers”. One of the two traveler wires between any two switches will carry line voltage and the other traveler of the pair will not carry line voltage. After a toggle of any switch in the electrical circuit, in one or more of the pair of traveler wires between the switches, the traveler carrying line voltage will shift to the other wire of the pair.
Dimmer switches can be used in electrical circuits wired for three-way switches and four-way switches. These switches are typically called “3-way dimmer” switches. In any given electrical circuit, typically there is only one switch containing dimming circuitry, performing the dimming or “load limiting” function. This switch is referred to as the “master dimmer” switch or simply as the “dimmer switch” or the “dimmer”. Additional switches called “accessory dimmers”, “auxiliary dimmers” or “remote dimmers” can be included in the electrical circuit to allow multiple switch locations to control the dim level of the load, but these additional switches are not dimmer switches but switches that communicate with the dimmer switch, able to command the dimmer switch to set the load to a particular dim level.
In an electrical circuit containing only two three-way switches, either of the two three-way switches can be replaced with a dimmer switch to control the dim level of the load. The dim level however can only then be controlled from the dimmer switch; the remaining three-way switch can only turn the load “on” or “off”. If the second three-way switch in that electrical circuit were replaced with a remote dimmer, one of the traveler wires would have to be used to communicate from the remote switch to the dimmer switch so that both switches could control the dim level of the load. The electrical circuit would then no longer be using conventional wiring for three-way switches. Similarly, in a circuit with two-three way switches and one or more four-way switches, if one switch is replaced with a dimmer switch, the wiring remains “conventional” and the remaining standard three-way and four-way switches will function in the electrical circuit albeit only to turn the load “on” or “off”. To allow more than one switch location to control the dim level of the load requires the use of remote dimmers. Since one of the travelers must then be used for the remote dimmers to communicate to the master dimmer, the wiring is no longer conventional and the other standard three-way and four way switches in the electrical circuit will no longer function. Consequently all of the remaining standard three-way and four-way switches must be replaced with remote dimmer switches.
Timer switches can be used in electrical circuits wired for three-way switches and four-way switches. These switches are typically used to save energy in office buildings, turning off lights at a preset time when the office is likely empty or used to turn lights “on” and “off” to give a “lived in” appearance to a home from the outside when homeowners are away.